1. Field of the Invention
The present invention relates to a method for pulsewise transmission triggering of a piezoelectric sound transducer with a definable pulse time and which is to be carried out with an electrical alternating voltage having a frequency which is equal to the self-resonance of the transducer.
2. Description of the Prior Art
It is known from the prior art to use this general technique from a pulse signal for distance measurements. For this purpose, short ultrasonic pulses are transmitted and the echo signal is received and evaluated. The distance of an object reflecting the ultrasonic pulses results from the transit time of the ultrasonic waves.
In the case of short distances, whereby the transit time is no longer greater by at least an order or magnitude than the pulse duration of the ultrasonic signal of the piezoelectric transducer, difficulties result for an accurate determination of the transit time, since the incipient time of the transmitted sound pulse cannot be determined with any type of random accuracy.
Previously, this problem was solved by using special evaluating methods. If the function of the initial sounding of the ultrasonic pulse is known, then by mathematical extrapolation of the envelope of the received signal, the beginning of the echo can be determined subsequently somewhat precisely. This method of a backward extrapolation, however, presumes the storage of the received signal and is thus expensive at the outset.